Process for the production of vinyl acetate

ABSTRACT

A process for the production of vinyl acetate comprising contacting in a first reaction zone a gaseous feedstock comprising essentially ethane with a molecular oxygen-containing gas in the presence of a catalyst to produce a first product stream comprising acetic acid; contacting in a second reaction zone a gaseous feedstock comprising essentially ethane with a molecular oxygen-containing gas in the product stream comprising ethylene; contacting in a third reaction one the first gaseous product stream and the second gaseous product stream with a molecular oxygen-containing gas in the presence of a catalyst to produce a fourth product stream comprising vinyl acetate; separating the product stream from step (3) and recovering vinyl acetate from said product stream from step (3).

This application is a 371 of PCT/EP00/04545 filed May 19, 2000.

STATE OF THE ART

The present invention relates generally to an integrated process for theproduction of vinyl acetate and in particular to an integrated processfor the production of vinyl acetate from a gaseous feedstock comprisingessentially ethane.

Vinyl acetate is generally prepared commercially by contacting aceticacid and ethylene with molecular oxygen in the presence of a catalystactive for the production of vinyl acetate. Suitably, the catalyst maycomprise palladium, an alkali metal acetate promoter and an optionalco-promoter (for example, gold or cadmium) on a catalyst support. Aceticacid produced by carbonylation generally requires extensive purificationto remove inter alia iodides arising from the catalyst system generallyemployed because iodides are recognised as potential vinyl acetatecatalyst poisoners.

Combinations of processes for producing vinyl acetate are known in theart. Thus, WO 98/105620 discloses a process for the production of vinylacetate and/or acetic acid which process comprises first contactingethylene and/or ethane with oxygen to produce a first product streamcomprising acetic acid, water and ethylene, contacting in a secondreaction zone in the presence or absence of additional ethylene and/oracetic acid the first product stream with oxygen to produce a secondproduct stream comprising vinyl acetate, water, acetic acid andoptionally ethylene; separating the product stream from the second stepby distillation into an overhead azeotrope fraction comprising vinylacetate and water and a base fraction comprising acetic acid; eitherrecovering acetic acid from the base fraction and optionally recyclingthe azeotrope fraction or recovering vinyl acetate from the azeotropefraction. The catalysts suggested in WO 98/05620 for the oxidation ofethylene to acetic acid or ethane to acidic acid are catalysts of theformulaPd_(a)M_(b)TiP_(c)O_(x)with M being selected from Cd, Au, Zn, Tl, alkali metals and alkalineearth metals; other catalysts for the oxidation of ethane to acetic acidare catalysts of the formulaVP_(a)M_(b)O_(x)with M being selected from Co, Cu, Re, Fe, Ni, Nb, Cr, W, U, Ta, Ti, Zr,Zn, Hf, Mn, Pt, Pd, Sn, Sb, Bi, Ce, As, Ag and Au or catalysts for theoxidation of ethane and/or ethylene to form ethylene and/or acetic acidwhich catalysts comprise the elements A, X and Y, wherein A isMo_(d)Re_(e)W_(f) and wherein X is Cr, Mn, Nb, Ta, V or W and wherein Yis Bi, Ce, Co, Cu, Fe, K, Mg, Ni, P, Pb, Sb, Si, Sn, Tl or U.

Other catalysts for the oxidation of ethane to acetic acid and ethylenesuggested in WO 98/05620 are those of the formulaMo_(x)V_(y)Z_(z)with Z being selected from Li, Na, Be, Mg, Ca, Sr, Ba, Zn, Cd, Hg, Sc,Y, La, Ce, Al, Tl, Ti, Zr, Hf, Pb, Nb, Ta, As, Sb, Bi, Cr, W, U, Te, Fe,Co, Ni.

U.S. Pat. No. 5,185,308 which is cited in WO 98/05620 describes exampleswherein space time yields in the range between 555 and 993 g vinylacetate per hour per liter catalyst are achieved.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide for an integratedprocess for the production of vinyl acetate from a gaseous feedstockcomprising essentially ethane as the only external carbon source of rawmaterial supply, the process exhibiting space/time yields in the rangeof from 100 to 2000 grams of vinyl acetate per hour per liter ofcatalyst, preferably 500 to 1500 grams of vinyl acetate per hour perliter of catalyst.

THE INVENTION

Accordingly the present invention provides an integrated process for theproduction of vinyl acetate which comprises the steps:

-   1) contacting in a first reaction zone a gaseous feedstock    comprising essentially ethane with a molecular oxygen-containing gas    in the presence of a catalyst to produce a first product stream    comprising acetic acid;-   2) contacting in a second reaction zone a gaseous feedstock    comprising essentially ethane with a molecular oxygen-cntaining gas    in the presence of a catalyst to produce a second product stream    comprising ethylene;-   3) contacting in a third reaction zone in the presence or absence of    additional ethylene or acetic acid the first gaseous product stream    and the second gaseous product stream with a molecular    oxygen-containing gas in the presence of a catalyst to produce a    fourth product stream comprising vinyl acetate;-   4) separating the product stream from step (3) and recovering vinyl    acetate from said product stream from step (3).

The process according to the invention is based on the findings that acertain class of catalysts is capable of converting ethane to eitheracetic acid or ethylene with a very high selectivity and very high spacetime yield. Such separate ethylene and acetic acid product streams canthan be mixed in the appropriate ratio and directly fed into a reactorto form vinyl acetate.

Using ethane instead of ethylene as feedstock has the advantage, that itis available in natural gas. In the process of natural gas work-up,several ethane-containing mixtures are obtained, which are usuallysimply flared off, but which all can be used as carbon feedstock forperforming the process of the present invention.

Of specific advantage in the integrated vinyl acetate process of thepresent invention is that, in principal, infrastructures, utilities, andother features can be combined, for example only a single feed gascompressor and off-gas scrubbing system is required whereas separateacetic acid and vinyl acetate processes each require their own feed gascompressor and off-gas scrubbing system.

By combining steps 1, 2 and 3 of the present invention, reducedintermediate storage requirements are needed as compared to two separateprocesses. All these advantages lead to reduced capital and operatingcosts.

According to the invention a gaseous feedstock comprising essentiallyethane is contacted in a first reaction zone with a molecularoxygen-containing gas in the presence of a catalyst active for theoxidation of ethane to acetic acid to produce a first product streamcomprising acetic acid.

The catalyst active for the oxidation of ethane to acetic acid maycomprise any suitable catalyst as described in DE-A 197 45 902 which isincorporated herein by reference. These catalysts are of the formulaMo_(a)Pd_(b)X_(c)Y_(d)wherein X and Y have the following meaning:

-   X is selected from one or more elements of the group consisting of    Cr, Mn, Nb, Ta, Ti, V, Te and W;-   Y is selected from one or more elements of the group consisting of    B, Al, Ga, In, Pt, Zn, Cd, Bi, Ce, Co, Rh, Ir, Cu, Ag, Au, Fe, Ru,    Os, K, Rb, Cs, Mg, Ca, Sr, Ba, Nb, Zr, Hf, Ni, P, Pb, Sb, Si, Sn, Tl    and U    and wherein a, b, c and are gram atom ratios and denote    -   a=1;    -   b=0.0001-0.01; preferably 0.0001-0.005    -   c=0.4-1; preferably 0.5-0.8 and    -   d=0.005-1; preferably 0.01-0.3.

Preferred catalysts are those wherein X is V and Y is Nb, Sb and Ca. Pdratios above the indicated gram atom limit favor the formation of carbondioxide; Pd ratios below the indicated gram atom limit favor theformation of ethylene and in consequence the formation of acetic acid. Acatalyst specifically preferred for the process according to theinvention is Mo_(1.00)Pd_(0.00075)V_(0.55)Nb_(0.09)Sb_(0.01)Ca_(0.01).

In the second reaction zone—which is spatially separate from the firstreaction zone—a gaseous feedstock comprising essentially ethane iscontacted with a molecular oxygen-containing gas in the presence of acatalyst active for the oxidation of ethane to ethylene to produce asecond product stream comprising ethylene.

The catalysts active for the oxidation of ethane to ethylene maycomprise the same catalysts as disclosed above for the oxidation ofethane to acetic acid. Both processes differ in their reactionconditions, especially in the total pressure, residence time and watercontent in the feed. The oxidation of ethane to acetic acid is morefavourable at higher total pressures compared to the oxidativedehydrogenation of ethane to ethylene. Acetic acid formation is thepreferred reaction product when feeding steam together with ethane andthe molecular oxygen containing gas, while steam can be facultativelyused for the oxidative dehydrogenation of ethane to ethylene, but it isnot absolutely necessary.

Preferred catalysts are those wherein X is V and Y is Nb, Sb and Ca. Pdratios above the indicated gram atom limit favour the formation ofcarbon dioxide; Pd ratios below the indicated gram atom limit favour theformation of ethylene. A catalyst specifically preferred for the processaccording to the invention isMo_(1.00)Pd_(0.00075)V_(0.55)Nb_(0.09)Sb_(0.01)Ca_(0.01).

Useful catalysts for the oxidative dehydrogenation of ethane to ethylenecan also be V—Al, V—Nb—Al, Cr—Nb—Al and Cr—Ta—Al based oxides which wereshortly described (Liu, Y.; Cong, P.; Doolen, R. D.; Turner, H. W.;Weinberg, H.; Second Int. Symposium on Deactivation and Testing ofCatalysts Presented Before the Division of Petroleum Chemistry, Inc.;219^(th) National Meeting, ACS, San Francisco, Calif., Mar. 26-31, 2000;298-302).

Moreover, several other patents describe more generally the oxidativedehydrogenation of paraffins. Three patents should be exemplary citedhere which describe the oxidative dehydrogenation of paraffins on Nioxide based catalysts. E. g., U.S. Pat. No. 4,751,342 describes the useof an alkali-doped Ni—P—Sn oxide catalyst, GB 2 050 188 describes Ni—Pbcatalysts, and U.S. Pat. No. 3,886,090 describes Ni—Mg oxide catalystswhich are modified with several other elements.

It is an advantage of the present invention that the ratio ofselectivity to acetic acid to selectivity to ethylene which is formed inthe first reaction zone can be varied within wide ranges, i.e. from 0 to95% each by changing reaction parameters such as reaction temperature,total pressure, partial pressures of reactants, residence time, etc.

The reactions in the first and the second reaction zone preferably arecarried out such that the amounts of acetic acid and ethylene formed inthese reactions are in an appropriate ratio so that the combined firstand second product stream can be directly fed into the third reactionzone to form vinyl acetate without the need to feed additional aceticacid or ethylene.

The catalysts active for the oxidation of ethane may be used supportedor unsupported. Examples of suitable supports include silica,diatomaceous earth, montmorillonite, alumina, silica alumina, zirconia,titania, silicon carbide, activated carbon, and mixtures thereof. Thecatalyst active for the oxidation of ethane may be used in the form of afixed or fluidised bed.

The molecular oxygen-containing gas used in all reaction zones may beair or a gas richer or poorer in molecular oxygen than air. A suitablegas may be, for example oxygen diluted with a suitable diluent, forexample nitrogen or carbon dioxide. Preferably the molecularoxygen-containing gas is fed to the first and second reaction zoneindependently from the ethane feedstock.

The ethane feedstock of the process of the present invention may besubstantially pure, or slightly diluted with other gases like the onebeeing generated by natural gas separation, i.e. e.g. 90 Wt-%(PERP-report “Natural Gas Liquids Extraction 94/95 S4, P. 60”) or may beadmixtures with one or more of nitrogen, carbon dioxide, hydrogen, andlow levels of C3/C4 alkenes/alkanes. Catalyst poisons like sulphurshould be excluded. Likewise is it advantageous to minimise the amountof acetylene. The amount of inert components is only limited byeconomics.

Step (1) of the process of the present invention may suitably be carriedout by passing ethane, the molecular oxygen-containing gas, steam and(if necessary) additional inerts through the catalyst. The amount ofsteam may suitably be in the range from 0 to 50 Vol %. The molar ratioof ethane to oxygen may suitably be in the range between 1:1 and 10:1,preferably between 2:1 and 8:1.

Step (1) of the process of the present invention may suitably be carriedout at a temperature from 200 to 500° C., preferably from 200 to 400° C.

Step (1) of the process of the present invention may suitably be carriedout at atmospheric or superatmospheric pressure, for example in therange from 1 to 100 bar, preferably from 1 to 50 bar.

Typically, ethane conversions in the range of 10 to 100%, especially 10to 40% may be achieved in step (1) of the process of the presentinvention, depending on the reactor concept of step 1, which can also bea reactor cascade with interstitial oxygen feed.

Typically, oxygen conversions in the range 90 to 100% may be achieved instep (1) of the process of the present invention.

In step (1) of the process of the present invention, the catalystsuitably has a productivity (“space time yield” =STY) in the range 100to 2000 grams of acetic acid per hour per liter of catalyst, preferablyin the range 100 to 1500 grams of acetic acid per hour per liter ofcatalyst.

Step (1) of the present invention can be carried out in fixed bed aswell as in fluidised bed reactors.

The gaseous product stream from step (1) comprises acetic acid andwater, and may contain ethane, ethylene, oxygen, nitrogen and theby-products, carbon monoxide and carbon dioxide. Usually, no or verysmall amounts (<100 ppm) of carbon monoxide are produced in step (1). Incase that carbon monoxide is produced in higher amounts up to 5%, itmay—if necessary—be removed after step (1), e.g. by adsorption or bycombustion to carbon dioxide by a molecular oxygen-containing gas. Theacetic acid is present in the gaseous product stream of step (1)preferably in an amount as is required for direct conversion to vinylacetate with the ethylene contained in the second product stream whichwill be combined with this first product stream.

Step (2) of the process of the present invention may suitably be carriedout by passing ethane, the molecular oxygen-containing gas, steam and(if necessary) additional inerts through the catalyst. The amount ofsteam may suitably be in the range from 0 to 50 Vol %. The molar ratioof ethane to oxygen may suitably be in the range between 1:1 and 10:1,preferably between 2:1 and 8:1.

Step (2) of the process of the present invention may suitably be carriedout at a temperature from 200 to 500° C., preferably from 200 to 400° C.

Step (2) of the process of the present invention may suitably be carriedout at atmospheric or superatmospheric pressure, for example in therange from 1 to 50 bar, preferably from 1 to 30 bar.

Typically, ethane conversions in the range of 10 to 100%, especially 10to 40% may be achieved in step (2) of the process of the presentinvention, depending on the reactor concept of step (2), which can alsobe a reactor cascade with interstitial oxygen feed.

Typically, oxygen conversions in the range 90 to 100% may be achieved instep (2) of the process of the present invention.

In step (2) of the process of the present invention, the catalystsuitably has a productivity (STY) in the range 100 to 2000 grams ofethylene per hour per liter of catalyst, preferably in the range 100 to1500 grams of ethylene per hour per liter of catalyst.

Step (2) of the present invention can be carried out in fixed bed aswell as in fluidised bed reactors.

The gaseous product stream from step (2) comprises ethylene and water,and may contain ethane, acidic acid, oxygen, nitrogen and theby-products, carbon monoxide and carbon dioxide. Usually, no or verysmall amounts (<100 ppm) of carbon monoxide are produced in step (2). Incase that carbon monoxide is produced in higher amounts up to 5%, itmay—if necessary—be removed after step (2), e.g. by adsorption or bycombustion to carbon dioxide by a molecular oxygen-containing gas. Theethylene is present in the gaseous product stream of step (2) preferablyin an amount as is required for direct conversion to vinyl acetate withthe acidic acid contained in the first product stream which will becombined with this second product stream.

The ethylene/acidic acid ratio which is necessary for feeding the vinylacetate reactor (step (3)) of the present invention may suitably beadjusted by changing the reaction parameters of step (1) and/or step(2), e.g. reaction temperature, total pressure, gaseous hourly spacevelocity, partial pressures of each reactant and, especially, by varyingthe steam partial pressure in the feed of step (1).

The gaseous product from step (1) and the gaseous product from step (2)may be fed directly to the third reaction zone of step (3) together withoptionally additional molecular oxygen-containing gas, optionallyadditional ethylene and optionally additional acetic acid, which canpreferably be taken from step (4), the vinyl acetate separation.

The catalyst active for the production of vinyl acetate which is used instep (3) of the process of the present invention may comprise anysuitable catalyst known in the art, for example, as described in GB 1559 540, U.S. Pat. No. 5,185,308 and WO 99/08791.

EP-A 0 330 853 describes catalysts for the production of vinyl acetateall-throughout impregnated containing Pd, K, Mn and Cd as additionalpromotor instead of Au.

GB 1 559 540 describes a catalyst active for the preparation of vinylacetate by the reaction of ethylene, acetic acid and oxygen, thecatalyst consisting essentially of:

-   (1) a catalyst support having a particle diameter of from 3 to 7 mm    and a pore volume of from 0.2 to 1.5 ml/g, a 10% by weight water    suspension of the catalyst support having a pH from 3.0 to 9.0,-   (2) a palladium-gold alloy distributed in a surface layer of the    catalyst support, the surface layer extending less than 0.5 mm from    the surface of the support, the palladium in the alloy being present    in an amount of from 1.5 to 5.0 grams per liter of catalyst, and the    gold being present in an amount of from 0.5 to 2.25 grams per liter    of catalyst, and-   (3) from 5 to 60 grams per liter of catalyst of alkali metal    acetate.

U.S. Pat. No. 5,185,308 describes a shell impregnated catalyst activefor the production of vinyl acetate from ethylene, acetic acid and anoxygen containing gas, the catalyst consisting essentially of

-   (1) a catalyst support having a particle diameter from about 3 to    about 7 mm and a pore volume of 0.2 to 1.5 ml per gram,-   (2) palladium and gold distributed in the outermost 1.0 mm thick    layer of the catalyst support particles, and-   (3) from about 3.5 to about 9.5% by weight of potassium acetate    wherein the gold to palladium weight ratio in said catalyst is in    the range 0.6 to 1.25.

WO 99/08791 describes a method for producing catalysts containing metalnanoparticles on a porous support, especially for gas phase oxidation ofethylene and acetic acid to form vinyl acetate. The invention relates toa method for producing a catalyst containing one or several metals fromthe group of metals comprising the sub-groups Ib and VIIIb of theperiodic table on porous support particles, characterised by a firststep in which one or several precursors from the group of compounds ofmetals from sub-groups Ib and VIIIb of the periodic table is or areapplied to a porous support, and a second step in which the porous,preferably nanoporous support to which at least one precursor has beenapplied is treated with at least one reduction agent, to obtain themetal nanoparticles produced in situ in the pores of said support.

Typically, step (3) of the process of the present invention is carriedout heterogeneously with the reactants being present in the gas phase.

The molecular oxygen-containing gas used in step (3) of the process ofthe present invention may comprise unreacted molecular oxygen-containinggas from step (1) or (2) and/or additional molecular oxygen-containinggas. Preferably, at least some of the molecular oxygen-containing gas isfed independently to the third reaction zone from the acetic acid andethylene reactants.

Step (3) of the process of the present invention may suitably be carriedout at a temperature in the range from 140 to 220° C.

Step (3) of the process of the present invention may suitably be carriedout at a pressure in the range from 1 to 100 bar.

Step (3) can be carried out in any suitable reactor design capable ofremoving the heat of reaction in an appropriate way; preferred technicalsolutions are fixed or fluidised bed reactors.

Acetic acid conversions in the range 5 to 50% may be achieved in step(3) of the process of the present invention.

Oxygen conversions in the range 20 to 100% may be achieved in step (3)of the present invention.

In step (3) of the process of the present invention, the catalystsuitably has a productivity (STY) in the range 100 to 2000 grams ofvinyl acetate per hour per liter of catalyst, but >10000 grams of vinylacetate per hour per liter of catalyst is also suitable.

The third product stream from step (3) of the process comprises vinylacetate and water and optionally also unreacted acetic acid, ethyleneethane, nitrogen, carbon monoxide, carbon dioxide and possibly presenttraces of other byproducts. Intermediate between step (3) and step (4)of the process of the invention it is preferred to remove ethylene, andethane, carbon monoxide and carbon dioxide, if any, from the thirdproduct stream, suitably as an overhead gaseous fraction from ascrubbing column, in which a liquid fraction comprising vinyl acetate,water and acetic acid is removed from the base.

The third product stream from step (3) comprising vinyl acetate, waterand acetic acid, with or without the intermediate scrubbing step, isseparated in step (4) by distillation into an overhead azeotropefraction comprising vinyl acetate and water and a base fractioncomprising acetic acid.

Vinyl acetate is recovered from the azeotrope fraction separated in step(3), suitably for example by decantation. The recovered vinyl acetatemay, if desired, be further purified in known manner. The base fractioncomprising acetic acid separated in step (3) is preferably recycled,with or preferably without further purification, to step (3) of theprocess.

The overall Space Time Yield (STY) of vinyl acetate (referred to ethane)produced in the process is in the range of 100 to 5000, preferably inthe range of 500 to 1500 grams of vinyl acetate per hour per liter ofcatalyst.

The overall yield may be adjusted in a number of ways includingindependently adjusting the reactant ratios and/or reaction conditionsof step (1) and/or step (2) and/or step (3) of the process, for exampleby independently adjusting the oxygen concentration(s) and/or thereaction temperatures and pressures.

The process of the present invention will now be illustrated by examplewith reference to FIG. 1 which represents in schematic form apparatusfor use in the process of the present invention.

The apparatus comprises a first reaction zone (1), a second reactionzone (2), a third reaction zone (3) and a scrubber column (4).

In use, a molecular oxygen-containing gas, optional steam and a gaseousfeedstock comprising essentially ethane (5) are fed to the firstreaction zone (1) which contains a catalyst active for the oxidation ofethane to form acetic acid. Depending on the scale of the process, thefirst reaction zone (1) may comprise either a single reactor or severalreactors in parallel or series. The first reaction zone may alsocomprise a reactor cascade, wherein between the individual reactorsadditional molecular oxygen-containing gas can be fed. A first gaseousproduct stream comprising acetic acid, unreacted feedstock, optionallyunconsumed molecular oxygen-containing gas and water together withcarbon monoxide, carbon dioxide, and inerts is withdrawn from the firstreaction zone (1).

The second reaction zone (2) is fed with a molecular oxygen-containinggas, optional steam and a gaseous feedstock comprising essentiallyethane (6). The reaction zone (2) contains a catalyst active for theoxidation of ethane to form ethylene. Depending on the scale of theprocess, the second reaction zone (2) may comprise either a singlereactor or several reactors in parallel or series. The second reactionzone may also comprise a reactor cascade, wherein between the individualreactors additional molecular oxygen-containing gas can be fed. A secondgaseous product steam comprising ethylene, unreacted feedstock,optionally unconsumed molecular oxygen-containing gas and water togetherwith carbon monoxide, carbon dioxide, and inerts is withdrawn from thesecond reaction zone (2).

The first and the second product stream are fed to the third reactionzone (3). Additional molecular oxygen-containing gas (7) may be mixedwith the product stream withdrawn from the first and the second reactionzone (1) and (2). In the third reaction zone (3) acetic acid andethylene are contacted with molecular oxygen-containing gas in thepresence of a catalyst active for the production of vinyl acetate.Depending on the scale of the process, the third reaction zone (3) maycomprise either a single reactor or several reactors in parallel or inseries. A product stream comprising vinyl acetate, water, optionallyethane, gaseous by-products and unreacted acetic acid and ethylene iswithdrawn from the third reaction zone (3) and is fed to the scrubbercolumn (4) where a gaseous stream comprising ethylene, and optionallyethane together with inerts, carbon monoxide and carbon dioxideby-products is withdrawn overhead and is recycled to the first or secondreaction zone (1)/(2). A liquid stream comprising vinyl acetate, water,unreacted acetic acid and possibly present other high boiling productsof the process are withdrawn from the base of the scrubber column (4)and vinyl acetate is isolated in state of the art equipment not shown.For example it is fed to a distillation column where vinyl acetate andwater is removed as an azeotrope and acetic acid, and possibly presentother high boiling products are removed as a bleed from the base of thedistillation column. The water in the overhead stream from thedistillation column can be separated from the vinyl acetate in adecanter and a vinyl acetate product stream removed from decanter ispurified by conventional means known in the art.

Carbon dioxide by-product can be removed by any viable technical processknown in the art e.g. by reversible absorption in an aqueous K₂CO₃solution which is regenerated in a desorption column (not shown).

The invention is illustrated in the following examples.

EXAMPLES

Preparation of Catalysts

Example (1)

Preparation of catalyst I:Mo_(1.00)Pd_(0.00075)V_(0.55)Nb_(0.09)Sb_(0.01)Ca_(0.01)O_(x)

-   Solution 1 80 g ammonium molybdate (Riedel-de Haen) in 400 ml water.-   Solution 2 29.4 g ammonium metavanadate (Riedel-de Haen) in 400 ml    water.-   Solution 3 19.01 g niobium ammonium oxalate (H. C. Starck),    -   1.92 g antimony oxalate (Pfaltz & Bauer), and    -   1.34 g calcium nitrate (Riedel-de Haen) in 200 ml water.-   Solution 4 0.078 g palladium(II)acetate (Aldrich) in 200 ml ethanol.

Solutions 1, 2 and 3 were stirred separately at 70° C. for 15 minutes.Then, solution 3 was poured into solution 2, and stirred together at 70°C. for another 15 minutes before adding this into solution 1.Thereafter, solution 4 was added.

The resulting mixture was evaporated to obtain a remaining total volumeof 800 ml. This mixture was spray-dried at 180° C. followed by dryingthe powder in static air at 120° C. for 2 hours and calcining at 300° C.for 5 hours.

Example (2)

Preparation of catalyst II: K,Pd,Au/TiO₂

2.11 g palladium acetate (Aldrich) and 1.32 g gold acetate weredissolved in 30 ml acetic acid. The preparation of the employed goldacetate is described e.g. in U.S. Pat. No. 4,933,204. 100 ml TiO₂support (P25 pellets, Degussa, Hanau) were added to the palladium andgold acetate solution. Then, the majority of acetic acid was evaporatedusing a rotary evaporator at 70° C., followed by evaporating the restusing an oil pump at 60° C. and finally in a vacuum drying cabinet at60° C. for 14 h.

The resulting pellets were reduced with a gas mixture of 10 Vol %hydrogen in nitrogen, while passing the gas (40 l/h) directly throughthe pellets at 500° C. and 1 bar for 1 h. For loading with potassiumions, the reduced pellets were added to a solution containing 4 gpotassium acetate in 30 ml of water, for 15 minutes in a mixingapparatus.

Then, the solvent was evaporated using a rotary evaporator. The pelletswere dried at 100° C. for 14 h.

Catalyst II was prepared in three batches using the same process; theyare called II a, II b and II c, respectively.

All catalysts were then pressed, broken and sieved into a granularfraction between 0.35 and 0.70 mm for performing the catalytic tests.

Catalytic Tests

For performing the catalytic reaction described in steps (1), (2) and(3) of the present invention, double-wall fixed bed reactors with aninner diameter of 14 mm and 20 mm, respectively, and a length of 350 mmwere used. The reactor was heated via the external tube with an oilbath. Typically, 5 ml and 15 ml of catalyst, respectively, partiallymixed with some inert material, e.g. typically glass, quartz or aluminagranules or beads in a catalyst to inert material volume ratio of e.g.2:1, 1:1, 1:2, 1:5. To decrease the dead volume of the reactor, it wasfilled up with inert material (as mentioned above) before and after thecatalyst bed. The volume flows were typically adjusted by mass andliquid flow controllers, respectively.

The analysis of reaction products was performed by on-line gaschromatography.

The results of catalytic measurements on catalysts I to XIII (examples(1 to 13)) for performing steps (1) and (2) of the present inventionusing one single reactor are shown in Tables 1 and 2. Measurements ofstep (1) (results presented in Table 1) were performed at 15 bar.

Data in Tables 1 and 2 are defined as follows:

-   Conversion of ethane    [%]=(0.5*[CO]+0.5*[CO₂]+[C₂H₄]+[CH₃COOH])/(0.5*[CO]+0.5*[CO₂]+[C₂H₄]+[C₂H₆]+[CH₃COOH])*100-   Selectivity to ethylene    [%]=([C₂H₄])/(0.5*[CO]+0.5*[CO₂]+[C₂H₄]+[CH₃COOH]*100-   Selectivity to acetic acid    [%]=([CH₃COOH])/(0.5*[CO]+0.5*[CO₂]+[C₂H₄]+[CH₃COOH])*100    with-   [ ]=concentration in mol %-   [C₂H₆]=concentration of ethane not converted-   τ[s]=catalyst volume (ml)/volume flow of the gas (ml/s) at reaction    conditions-   STY=g product/(I catalyst*h)

TABLE 1 Catalytic results on catalyst I performing the ethane oxidationto acetic acid Results Space Time Reaction Conditions Selectivity YieldFeed Composition Conversion S S S STY Run T t V(C₂H₅) V(O₂) V(N₂) V(H₂O)X(C₂H₅) (HOAc) (C₂H₄) (CO + CO₂) (HOAc) No. [° C.] [s] [ml/s] [ml/s][ml/s] [ml/h] [%] [%] [%] [%] [g/(h)] 1 280 14.8  1.0 0.2 0.8 1.4 13.391.5 0.7 7.8 235 2 280 7.4 2.0 0.4 1.6 2.9 10.5 90.4 3.5 6.0 362 3 3007.1 2.0 0.4 1.6 2.9 13.2 89.0 2.0 9.0 447 4 300 4.8 3.0 0.6 2.4 4.3 11.387.2 5.5 7.3 564 5 300 4.1 3.5 0.7 2.8 5.0 10.2 86.2 7.4 6.4 584 6 3003.7 4.0 0.8 3.2 5.0  9.9 84.1 9.2 6.6 630

Catalyst II (example (2)) was used in step (3) of the present inventionfor the production of vinyl/acetate. The catalytic test was performed atreaction temperatures in the range from 150 to 170° C., at reactionpressures from 8 to 9 bar.

The results of catalytic measurements on catalyst II (example (2)) forperforming step (3) of the present invention are shown in Table 2.

Data in Table 2 are defined as follows;

-   Selectivity to vinyl acetate (VAM)    [%]=([VAM])/([VAM]+0.5*[CO]+0.5*[CO₂])*100    with-   [ ]=concentration in mol %-   STY=g product/(I catalyst*h)

TABLE 2 Catalytic results on catalyst II performing the vinyl acetatesynthesis Reaction Results Conditions Selectivity Space Time Yield No. T[°C] P [bar] S (VAM) [%] STY [g/(h)] a 155 9 98 1000 a 160 9 98 1050 a170 9 96 1000 b 160 9 98 1150 b 170 9 97  700 c 170 9 98 1300

1. An integrated process for the production of vinyl acetate whichcomprises the steps of: 1) contacting in a first reaction zone a gaseousfeedstock comprising mainly ethane with a molecular oxygen-containinggas in the presence of a catalyst to produce a gaseous product streamcomprising acetic acid; 2) contacting in a second reaction zone agaseous feedstock comprising mainly ethane with a molecularoxygen-containing gas in the presence of a catalyst to produce a secondgaseous product stream comprising ethylene; 3) contacting in a thirdreaction zone the first gaseous product stream and the second gaseousproduct stream with a molecular oxygen-containing gas in the presence ofa catalyst to produce a fourth product stream comprising vinyl acetate;4) separating the product stream from step (3) and recovering vinylacetate from said product stream from step (3) wherein the catalyst inthe first and second reaction zone is of the formulaMo_(a)Pd_(b)X_(c)Y_(d)  wherein X and Y have the following meaning: X isat least one element selected from the group consisting of Cr, Mn, Nb,Ta, Ti, V, Te and W: Y is at least one element selected from the groupconsisting of B, Al, Ga, In, Pt, Zn, Cd, Bi, Ce, Co, Rh, Ir, Cu, Ag, Au,Fe, Ru, Os, K, Cs, Mg, Ca, Sr, Ba, Nb, Zr, Hf, Ni, P, Pb, Sb, Si, Sn, TIand U and wherein a, b, and c are gram atom ratios and denote a=1;b=0.000-0.1; c=0.1-1; d=0.005-1.
 2. The process according to claim 1wherein gaseous feedstock for step (1) comprises ethane, molecularoxygen-containing with an ethane to oxygen ratio in the range between1:1 and 10:1 and 0 to 50 Vol-% steam (based on the total volume of thegaseous feedstock).
 3. The process according to claim 1 wherein thegaseous feedstock for step (2) comprises ethane, molecularoxygen-containing gas with an ethane to oxygen ratio in the rangebetween 1:1 and 10:1.
 4. The process according claim 1 whereinadditional ethylene and/or acetic acid from recycle gas is fed to thethird reaction zone.
 5. The process according to claim 1 wherein themolecular oxygen-containing gas is fed to the first and/or secondreaction zone independently from the ethane feedstock.
 6. The processaccording to claim 1 wherein the molecular oxygen-containing gas is fedindependently to the third reaction zone from the acetic acid andethylene reactants.
 7. The process of claim 1 wherein b is 0.0001 to0.0005, c is 0.5 to 0.8 and d is 0.01 to 0.3.